Oxynitride compounds, methods of preparation, and uses thereof

ABSTRACT

Oxynitride nanoparticles, methods of preparation thereof, and methods of use thereof are disclosed. One representative oxynitride nanoparticle includes a M x O y N z  nanoparticle, where x is in the range of about 1 to 3, y is in the range of about 0.5 to less than 5, and z is in the range of about 0.001 to 0.5.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to copending U.S. ProvisionalApplication entitled, “Generation of TiO_(2−x)N_(x) Photocatalysts fromthe Solution Phase Nitration of TiO₂”, filed with the United StatesPatent and Trademark Office on Dec. 21, 2001, and assigned Ser. No.60/342,947, which is entirely incorporated herein by reference.

TECHNICAL FIELD

The present invention is generally related to oxide compounds and, moreparticularly, is related to oxynitride compounds and methods ofpreparation thereof.

BACKGROUND OF THE INVENTION

The initial observation of the photoinduced decomposition of water ontitanium dioxide (TiO₂) has promoted considerable interest in solarcells and the semiconductor-based photocatalytic decomposition of waterand of other organic materials in polluted water and air. A continuedfocus on TiO₂ has resulted because of its relatively high reactivity andchemical stability under ultraviolet excitation (wavelength<387nanometers), where this energy exceeds the bandgaps of both anatase (3.2eV) and rutile (3.0 eV) crystalline n-TiO₂.

However, both anatase and rutile TiO₂ crystals are poor absorbers in thevisible region (wavelength>380 nm) and the cost and accessibility ofultraviolet photons make it desirable to develop photocatalysts that arehighly reactive under visible light excitation, utilizing the solarspectrum or even interior room lighting.

With this focus, several attempts have been made to lower the bandgapenergy of crystalline TiO₂ by transition metal doping and hydrogenreduction. One approach has been to dope transition metals into TiO₂ andanother has been to form reduced TiO_(x) photocatalysts. However, dopedmaterials suffer from a thermal instability, an increase ofcarrier-recombination centers, or the requirement of an expensiveion-implantation facility. Reducing TiO₂ introduces localized oxygenvacancy states below the conduction band minimum of titanium dioxide sothat the energy levels of the optically excited electrons will be lowerthan the redox potential of the hydrogen evolution and the electronmobility in the bulk region will be small because of the localization.

Films and powders of titanium oxynitride (TiO_(2−x)N_(x)) have revealedan improvement over titanium dioxide under visible light in opticalabsorption and photocatalytic activity such as photodegradation ofmethylene blue and gaseous acetaldehyde, and hydrophilicity of the filmsurface. Substitutional doping of nitrogen by sputtering a titaniumdioxide target in a nitrogen/argon gas mixture has been accomplished.After being annealed at 550° C. in nitrogen gas for four hours, thefilms were crystalline with features assignable to a mixed structure ofthe anatase and rutile crystalline phases. The films were yellowish incolor and their optical absorption spectra showed them to absorb lightbetween 400–500 nm, whereas films of pure titanium dioxide did not.Photocalytic activity for the decomposition of methylene blue showsactivity of TiO_(2−x)N_(x) at wavelengths less than 500 nm.

The active wavelength of TiO_(2−x)N_(x) of less than 500 nm promises awide range of applications, as it covers the main peak of the solarirradiation energy beyond Earth's atmosphere. Further, it is anexcellent light source, peaking at 390 to 420 nm, provided byrecently-developed light-emitting indium gallium nitride diodes.

In addition, nitrogen can be incorporated into the TiO₂ structure by thenitridation reaction of TiO₂ nanopowders that are subjected to a ammonia(NH₃) gas flow at about 600° C. Transmission electron microscopemicrographs showed that the synthesized TiN powder consisted of uniformspherical particles with an average diameter of about 20 nm whennitridation was performed at a temperature of about 600° C. for 2–5hours. No results with respect to the photocatalytic activity of thismaterial were presented.

The synthesis of chemically modified n-type TiO₂ by the controlledcombustion of Ti metal in a natural gas flame at a temperature of about850° C. represented another attempt at lowering the band gap energy ofTiO₂. The modified films were dark gray, porous in structure and with anaverage composition of n-TiO_(2−x)C_(x) (with x about 0.15). Thismaterial absorbs light at wavelengths below 535 nm and has a lowerband-gap energy than rutile TiO₂ (2.32 versus 3.00 electron volts). Whenilluminated with a 150 Watt xenon (Xe) lamp, and at an applied potentialof 0.3 volt, the chemically modified n-TiO_(2−x)C_(x) (with x about0.15) exhibited a higher water photoconversion efficienty (8.3%) thanthat of pure TiO₂ illuminated under the same conditions (1%).

All these examples require the use of very high temperature synthesisconditions, and long periods of time to produce these materials. Thetime and temperature previously required to make the TiO_(2−x)N_(x) andTiO_(2−x)C_(x) compounds makes these techniques costly and inefficient.

Thus, a heretofore unaddressed need exists in the industry for a simplemore cost effective method to fabricate novel materials capable ofexhibiting photo catalytic activity such as the photo-induceddecomposition of water and pollutants. Additionally, a need exists forbetter methods for their use in the production of electricity throughsolar cells, as well as to address some of the aforementioneddeficiencies and/or inadequacies.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide for oxynitridenanoparticles, methods of preparation thereof, and methods of usethereof. One representative of an embodiment of a nanostructure of thepresent invention includes a M_(x)O_(y)N_(z) nanoparticle, wherein x isin the range of about 1 to 3, y is in the range of about 0.5 to lessthan 5, and z is in the range of about 0.001 to about 0.5.

Another embodiment of the present invention provides for methods offorming oxynitride nanostructures. An exemplary method includesproviding at least one type of M_(h)O_(i) nanoparticle, wherein h is inthe range of about 1 to 3 and i is in the range of about 1 to 5;providing a solution of an alkyl amine; and mixing the at least one typeof M_(h)O_(i) nanoparticle and the solution of alkyl amine until areaction between the at least one type of M_(h)O_(i) nanoparticle andalkyl amine is substantially complete.

Other systems, methods, features, and advantages of the presentinvention will be or become apparent to one with skill in the art uponexamination of the following drawings and detailed description. It isintended that all such additional systems, methods, features, andadvantages be included within these descriptions, be within the scope ofthe present invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the invention can be better understood with reference tothe following drawings. The components in the drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present invention. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1A is a low resolution transmission electron micrograph (TEM) imageof titanium oxynitride nanostructures. FIG. 1B is a high resolution (HR)TEM image showing the polycrystalline character and lattice planes ofthe sample. The HR TEM image corresponds to an anatase crystal structureconfirmed by the x-ray powder diffraction pattern shown in the inset.

FIG. 2 includes (a) a reflection spectrum for Degussa P25™ TiO₂ whosespectrum rises sharply at 380 nanometers (nm), (b) a reflection spectrumof titanium oxynitride nanoparticles (3–11 nm) whose spectrum risessharply at 450 nm, and (c) a reflection spectrum of titanium oxynitridepartially agglomerated nanoparticles whose spectrum rises sharply at 550nm.

FIG. 3 includes (a) an infrared spectrum for triethylamine showing aclear C—H stretch region, and (b) an infrared spectrum of titaniumoxynitride nanoparticles (3–11 nm) corresponding to the yellow titaniumoxynitride crystallites whose reflection spectrum rises sharply at 450nm.

FIG. 4 is an XPS spectrum for untreated titanium dioxide nanoparticlesand titanium oxynitride nanoparticles. The nitrogen peak, which ispresent in the titanium oxynitride nanoparticle sample, but not in theuntreated titanium dioxide, is considerably more pronounced for thepalladium treated titanium oxynitride nanoparticles.

FIG. 5A is an XRD powder pattern for untreated titanium dioxide powders.FIG. 5B is an XRD powder pattern for titanium oxynitride partiallyagglomerated nanoparticles corresponding with the sharply risingreflectance spectrum at 550 nm. While the XRD patterns in FIGS. 5A and5B are indicative of the anatase phase, the broad XRD pattern forpalladium treated titanium oxynitride may be attributed to a structuraltransformation.

FIG. 6A is a TEM of a palladium metal impregnated titanium oxynitridenanostructure. FIG. 6B is a TEM micrograph of a dark brown-black crystalphase accompanying the palladium impregnated nitride nanostructures. Thedark crystallites are associated with a structural transformation (e.g.,the analog of octahedrite in titanium dioxide).

FIG. 7A is a graph illustrating the photodegradation of methylene bluein water at pH 7 and at about 390 nm. FIG. 7B is a graph illustratingthe photodegredation of methylene blue in water at pH 7 and at about 540nm.

DETAILED DESCRIPTION

Embodiments of the present invention provide for oxynitridenanoparticles having the following formula: M_(x)O_(y)N_(z), where M isa metal, a metalloid, a lanthanide, or an actinide, O is oxygen, N isnitrogen, x can range from about 1 to 3, y is about 0.5 to less than 5and z is about 0.001 to 0.5, about 0.001 to 0.2, and about 0.001 to 0.1.

Another embodiment of the present invention provides for methods ofpreparation of M_(x)O_(y)N_(z) nanoparticles. An exemplary method ofpreparing M_(x)O_(y)N_(z) nanoparticles includes mixing at least onetype of oxide nanoparticle (described below) with at least one alkylamine at room temperature until the reaction between the oxidenanoparticle and alkyl amines is substantially complete (e.g., typicallyless than 60 seconds). The result is the formation of M_(x)O_(y)N_(z)nanoparticles. Subsequently, the M_(x)O_(y)N_(z) nanoparticles can bedried in a vacuum and stored for use in the future.

In addition, another embodiment provides for oxynitride nanoparticleshaving the following formula: M1_(x1)M2_(x2)O_(y)N_(z), where M1 and M2can be a metal, a metalloid, a lanthanide, an actinide, or combinationsthereof; x1 and x2 are in the range from about 1 to 3; y is about 0.5 toless than 5; and z is about 0.001 to 0.5. Another embodiment providesfor methods of preparing M1_(x1)M2_(x2)O_(y)N_(z) nanoparticles. Themethod is similar to the method described above in regard toM_(x)O_(y)N_(z) nanoparticles and will be described in more detailbelow.

Another embodiment of the present invention provides for M_(x)O_(y)N_(z)nanoparticles having catalytic metal (M_(x)O_(y)N_(z)[M_(CAT)]) disposedthereon and/or therein. A representative method of the preparation ofM_(x)O_(y)N_(z)[M_(CAT)] nanoparticles includes mixing at least one typeof oxide nanoparticle with at least one alkyl amine and a catalyticmetal compound until the reaction between the oxide nanoparticle, alkylamines, and catalytic metal compound is substantially complete (e.g.,typically less than 60 seconds). The result is the formation ofM_(x)O_(y)N_(z)[M_(CAT)] nanoparticles. Subsequently, theM_(x)O_(y)N_(z)[M_(CAT)] particles can be vacuum dried and stored foruse in the future.

In addition, another embodiment provides for M1_(x1)M2_(x2)O_(y)N_(z)nanoparticles having catalytic metal (M1_(x1)M2_(x2)O_(y)N_(z)[M_(CAT)]) disposed thereon and/or therein and methods of formationthereof. The method is similar to the method described above in regardto M_(x)O_(y)N_(z)[M_(CAT)] nanoparticles and will be discussed in moredetail below.

Other embodiments of the present invention include the use of one ormore types of M_(x)O_(y)N_(z), M_(x)O_(y)N_(z) [M_(CAT)],M1_(x1)M2_(x2)O_(y)N_(z), and/or M1_(x1)M2_(x2)O_(y)N_(z) [M_(CAT)]nanoparticles in catalysts, for photocatalytic reactors, inphotocatalytic supports, in solar panel energy systems, and in pigments.

For example, one or more types of M_(x)O_(y)N_(z), M_(x)O_(y)N_(z)[M_(CAT)], M1_(x1)M2_(x2)O_(y)N_(z), and/or M1_(x1)M2_(x2)O_(y)N_(z)[M_(CAT)] nanoparticles can be used as a photocatalyst for convertingwater into hydrogen and oxygen. In addition, one or more types ofM_(x)O_(y)N_(z), M_(x)O_(y)N_(z) [M_(CAT)], M1_(x1)M2_(x2)O_(y)N_(z),and/or M1_(x1)M2_(x2)O_(y)N_(z) [M_(CAT)] nanoparticles can be used inthe photodegradation of organic molecules present in polluted water andair.

In particular, TiO_(2−x)N_(x) and/or TiO_(2−x)N_(x)[Pd] nanoparticlescan be used in photocatalytic reactors, solar cells, and pigments. Forexample, the TiO_(2−x)N_(x) and/or TiO_(2−1x)N_(x)[Pd] nanoparticles canbe incorporated into porous silicon structures (e.g., micro/nanoporousstructures) and act as a catalyst, a photocatalyst, or an electrodematerial.

M_(x)O_(y)N_(z) Nanoparticles

Embodiments of the M_(x)O_(y)N_(z) nanoparticles include, but are notlimited to, the following formulas: MO_(1−s)N_(s) (where s is in therange of about 0.001 to 0.5), MO_(2−t)N_(t) (where t is in the range ofabout 0.001 to 0.5), M₂O_(3−u)N_(u) (where u is in the range of about0.001 to 0.5), M₃O_(4−v)N_(v) (where v is in the range of about 0.001 to0.5), and M₂O_(5−w)N_(w) (where w is in the range of about 0.001 to0.5). In addition, the M_(x)O_(y)N_(z) nanoparticles are less than about40 nanometers (nm) in diameter, in the range of about 8 nm to 40 nm, inthe range of about 15 nm to 35 nm, and in the range of about 20 nm to 30nm.

As indicated above, M includes the transition metals, the metalloids,the lanthanides, and the actinides. More specifically, M includes, butis not limited to, titanium (Ti), zirconium (Zr), hafnium (Hf), tin(Sn), nickel (Ni), cobalt (Co), zinc (Zn), lead (Pb), molybdenum (Mo),vanadium (V), aluminum (Al), niobium (Nb), tantalum (Ta), silicon (Si),silver (Ag), iridium (Ir), platinum (Pt), palladium (Pd), gold (Au), orcombinations thereof. In particular, M can be Ti, Zr, Hf, Si, and Snand, preferably, M is Ti.

Embodiments of the M_(x)O_(y)N_(z) nanoparticles include, but are notlimited to, TiO_(2−t)N_(t) nanoparticles, ZrO_(2−t)N_(t) nanoparticles,HfO_(2−t)N_(t) nanoparticles, SiO_(2−t)N_(t) nanoparticles, andSnO_(2−t)N_(t) nanoparticles.

Embodiments of the M_(x)O_(y)N_(z) nanoparticles have the characteristicthat they are able to absorb radiation (i.e., light) in the range ofabout 350 nm to 2000 nm, about 500 nm to 2000 nm, about 540 nm to 2000nm, about 450 nm to 800 nm, about 500 nm to 800 nm, about 540 nm to 800nm, and about 540 nm to 560 nm. Preferably, the M_(x)O_(y)N_(z)nanoparticles absorb radiation at about 550 nm, the peak of the solarspectrum.

In general, the M_(x)O_(y)N_(z) nanoparticles may maintain their crystalstructure upon nitridation. However, some embodiments of theM_(x)O_(y)N_(z) nanoparticles may experience crystal phasetransformation. In particular, nitridation of anatase TiO₂ nanoparticlesdoes not appear to induce phase transformation whereas nitridation ofTiO₂ nanoparticles in the presence of PdCl₂ results in a structuraltransformation (i.e., transformation from the anatase crystal phase to acomplex mixed structural phase).

Methods of Making M_(x)O_(y)N_(z) Nanoparticles

Embodiments of the present invention also include methods of preparingM_(x)O_(y)N_(z) nanoparticles. An embodiment of a representative methodincludes mixing at room temperature at least one type of oxidenanoparticle (M_(h)O_(i) nanoparticles (where h is in the range of about1 to 3 and i is in the range of about 1 to 5)) with an excess of asolution having at least one type of alkyl amine. The solution can alsocontain hydrazine and/or ammonia.

In general, the M_(h)O_(i) nanoparticles have a diameter of less thanabout 40 nm and less than about 30 nm. The M_(h)O_(i) nanoparticles maybe in several forms. In particular, the M_(h)O_(i) nanoparticles can besuspended in a colloidal solution of one or more types of M_(h)O_(i)nanoparticles; a gel of one or more types of M_(h)O_(i) nanoparticles;one or more types of M_(h)O_(i) nanoparticles; or combinations thereof.

For M_(h)O_(i) nanoparticles, M includes the transition metals, themetalloids, the lanthanides, and the actinides. More specifically, Mincludes, but is not limited to, Ti, Zr, Hf, Sn, Ni, Co, Zn, Pb, Mo, V,Al, Nb, Ta, Si, Ag, Ir, Pt, Pd, Au, or combinations thereof. Inparticular, M can be Ti, Zr, Hf, Si, and Sn and, preferably, M is Ti.

The alkyl amine can include, but is not limited to, compounds having theformula of N(R₁)(R₂)(R₃). R₁, R₂, and R₃ can each be selected fromgroups such as, but not limited to, a methyl group, an ethyl group, apropyl group, and a butyl group. The preferred alkyl amine istriethylamine. In general, an excess amount (based on the quantity ofM_(h)O_(i) nanoparticles) of alkyl amine is included in the mixture toensure complete reaction of the M_(h)O_(i) nanoparticles. However, it iscontemplated and within the scope of this disclosure that amounts lessthan an excess of alkyl amine can be included in the mixture to produceM_(x)O_(y)N_(z) nanoparticles.

Subsequent to providing M_(h)O_(i) nanoparticles and the alkyl amine,the M_(h)O_(i) nanoparticles and the alkyl amine can be mixed in acontainer, preferably a closed glass container with a magnetic stirringrod. Alternatively, the mixture can be mixed by shaking the containerwith a machine or by hand. The M_(h)O_(i) nanoparticles and the alkylamine are mixed until reaction between them is substantially complete,which may be indicated by an exothermic reaction (i.e., heat release)and/or by a color change of the mixture. The reaction typically takesless than 60 seconds and, preferably, less than 10 seconds to formM_(x)O_(y)N_(z) nanoparticles.

After the reaction between the M_(h)O_(i) nanoparticle and the alkylamine is complete, the mixture is allowed to air dry. Subsequently, themixture is dried under a vacuum (about 5×10⁻² torr) for less thanapproximately 12 hours. The M_(x)O_(y)N_(z) nanoparticles are typicallycolored (e.g., a yellow to orange/red color for titanium oxynitrideparticles).

M_(x)O_(y)N_(z) [M_(CAT)] Nanoparticles

M_(x)O_(y)N_(z) [M_(CAT)] nanoparticles include M_(x)O_(y)N_(z)nanoparticles (as described above in reference to M_(x)O_(y)N_(z)nanoparticles) having one or more catalytic metals (M_(CAT)) disposedthereon and/or incorporated therein. The M_(CAT) can be a metal such as,but not limited to, palladium (Pd), silver (Ag), ruthenium (Rh),platinum (Pt), cobalt (co), copper (Cu), or iron (Fe).

It appears that the M_(CAT) can be incorporated onto (or impregnates)the M_(x)O_(y)N_(z) nanoparticles structure and/or the M_(CAT) can bedispensed on the surface of the M_(x)O_(y)N_(z) nanoparticles to formM_(x)O_(y)N_(z) [M_(CAT)] nanoparticles. In addition, the M_(CAT) canpromote the alteration of the crystal structure of the M_(x)O_(y)N_(z)nanoparticles. In one embodiment, the crystal structure of the TiO₂nanoparticles changes from an anatase crystal structure to a complexstructural mixture, which may include octahedrite crystal (e.g.,TiO_(2−t)N_(t)[Pd] (where t is in the range of about 0.001 to 0.5)).This transformation of structure takes place upon reaction of the TiO₂nanoparticles with an alkyl amine and PdCl₂.

Embodiments of the M_(x)O_(y)N_(z) [M_(CAT)] nanoparticles may have thecharacteristic that they are able to absorb radiation (i.e., light) inthe range of about 350 nm to about 2000 nm, about 500 nm to 2000 nm,about 540 nm to 2000 nm, about 450 nm to about 800 nm, about 500 nm to800 nm, about 540 nm to 800 nm, and about 540 nm to 560 nm. Preferably,the M_(x)O_(y)N_(z) [M_(CAT)] nanoparticles may absorb radiation atabout 550 nm, the peak of the solar spectrum.

Methods of Making M_(x)O_(y)N_(z) [M_(CAT)] Nanoparticles

Another embodiment of the present invention includes preparingM_(x)O_(y)N_(z)[M_(CAT)] nanoparticles by mixing at room temperature atleast one type of M_(h)O_(i) nanoparticle, a catalytic metal compound,and an excess of a solution having at least one type of alkyl amine.After the reaction between the at least one type of M_(h)O_(i)nanoparticle, the catalytic metal compound, and the at least one type ofalkyl amine is substantially complete, the mixture is allowed to airdry. Subsequently, the mixture is dried under a vacuum (about 5×10⁻²torr) for less than 12 hours. The resulting M_(x)O_(y)N_(z) [M_(CAT)]nanoparticles are typically colored (i.e., a brown-black color fortitanium oxynitride particles having Pd metal disposed thereon(TiO_(2−x)N_(x)[Pd])).

The catalytic metal compound can include compounds such as, but notlimited to, palladium chloride (PdCl₂), silver chloride (AgCl),ruthenium chloride (RhCl₄), platinum chloride (PtCl₂), cobalt chloride(CoCl₂), copper chloride (CuCl₂), and iron chloride (FeCl₂). Notintending to be bound by theory, it appears that the catalytic metalcompound may serve one or more purposes. For example, the catalyticmetal compound catalyzes the reaction of the M_(h)O_(i) nanoparticlesand the alkyl amine, as well as the increased uptake of nitrogen to formM_(x)O_(y)N_(z) [M_(CAT)] nanoparticles.

M1_(x1)M2_(x2)O_(y)N_(z) Nanoparticles

Another embodiment of the present invention provides for oxynitridenanoparticles having the following formula: M1_(x1)M2_(x2)O_(y)N_(z),where x1 and x2 are in the range from about 1 to 3, y is about 0.5 toless than 5, and z is about 0.001 to less than 5.

For the M1_(x1)M2_(x2)O_(y)N_(z) nanoparticles, M1 and M2 can includethe transition metals, the metalloids, the lanthanides, the actinides,or combinations thereof. More specifically, M1 and M2 include, but arenot limited to, Ti, Zr, Hf, Sn, Ni, Co, Zn, Pb, Mo, V, Al, Nb, Ta, Si,Ag, Ir, Pt, Pd, Au, or combinations thereof. In particular, M1 and M2can be Ti, Zr, Hf, Si, and Sn, or combinations thereof.

Embodiments of the M1_(x1)M2_(x2)O_(y)N_(z) nanoparticles may have thecharacteristic that they are able to absorb radiation (i.e., light) inthe range of about 350 nm to 2000 nm, about 500 nm to 2000 nm, about 540nm to 2000 nm, about 450 nm to 800 nm, about 500 nm to 800 nm, about 540nm to 800 nm, and about 540 nm to 560 nm. Preferably, theM1_(x1)M2_(x2)O_(y)N_(z) nanoparticles may absorb radiation at about 550nm, the peak of the solar spectrum.

Methods of Making M1_(x1)M2_(x2)O_(y)N_(z) Nanoparticles

Embodiments of the present invention also include methods of preparingM1_(x1)M2_(x2)O_(y)N_(z) nanoparticles. An embodiment of arepresentative method includes mixing at room temperature two types ofoxide nanoparticles (M_(h)O_(i) nanoparticles (where h is in the rangeof about 1 to 3 and i is in the range of about 1 to 5)) with an excessof a solution having at least one type of alkyl amine. The solution canalso contain hydrazine and/or ammonia.

Subsequently, the two types of M_(h)O_(i) nanoparticles and the alkylamine can be mixed in a container, preferably a closed glass container,with a magnetic stirring rod. Alternatively, the mixture can be mixed byshaking the container with a machine or by hand. The two types ofM_(h)O_(i) nanoparticles and the alkyl amine are mixed until thereaction is substantially complete, which may be indicated by anexothermic reaction (i.e., heat release) and/or by a color change of themixture. After the reaction between the two types M_(h)O_(i)nanoparticles and the alkyl amine is complete, the mixture is allowed toair dry. Subsequently, the mixture is dried under a vacuum (about 5×10⁻²torr) for less than 12 hours.

Another representative method includes mixing a mixed oxide nanoparticlehaving the following formula: M1_(h1)M2_(h2)O_(i) (where h1 and h2 canrange from about 1 to 3 and i is in the range of about 1 to 5), with anexcess of a solution having at least one type of alkyl amine. Thesolution can also contain hydrazine and/or ammonia.

Subsequently, the M1_(h1)M2_(h2)O_(i) nanoparticles and the alkyl aminecan be mixed in a container, preferably a closed glass container, with amagnetic stirring rod. Alternatively, the mixture can be mixed byshaking the container with a machine or by hand. The M1_(h1)M2_(h2)O_(i)nanoparticles and the alkyl amine are mixed until the reaction issubstantially complete, which may be indicated by an exothermic reaction(i.e., heat release) and/or by a color change of the mixture. After thereaction of the M1_(h1)M2_(h2)O_(i) nanoparticles and the alkyl amine iscomplete, the mixture is allowed to air dry. Subsequently, the mixtureis dried under a vacuum (about 5×10⁻² torr) for less than 12 hours.

M, M1, M2, and the alkyl amines correspond to the descriptions providedabove and will not be described here in any more detail.

M1_(x1)M2_(x2)O_(y)N_(z)[M_(CAT)] Nanoparticles

M1_(x1)M2_(x2)O_(y)N_(z)[M_(CAT)] nanoparticles includeM1_(x1)M2_(x2)O_(y)N_(z) nanoparticles described above in reference toM1_(h1)M2_(h2)O_(i) nanoparticles) having one or more catalytic metals(M_(CAT)) disposed thereon and/or incorporated therein. As describedabove, the M_(CAT) can be a metal such as, but not limited to, Pd, Ag,Rh, Pt, Co, Cu, or Fe.

Embodiments of the M1_(x1)M2_(x2)O_(y)N_(z)[M_(CAT)] nanoparticles mayhave the characteristic that they are able to absorb radiation (i.e.,light) in the range of about 350 nm to 2000 nm, about 500 nm to 2000 nm,about 540 nm to 2000 nm, about 450 nm to 800 nm, about 540 nm to 800 nm,about 500 nm to 800 nm, and about 540 nm to 560 nm. Preferably, theM1_(x1)M2_(x2)O_(y)N_(z)[M_(CAT)] nanoparticles may absorb radiation atabout 550 nm, the peak of the solar spectrum.

Methods of Making M1_(x1)M2_(x2)O_(y)N_(z)[M_(CAT)] Nanoparticles

Another embodiment of the present invention includes preparingM1_(x1)M2_(x2)O_(y)N_(z)[M_(CAT)] nanoparticles. A representative methodincludes mixing at room temperature two types of M_(h)O_(i)nanoparticles with a catalytic metal compound and an excess of asolution having at least one type of alkyl amine. The solution can alsocontain hydrazine and/or ammonia.

Subsequently, the two types of M_(h)O_(i) nanoparticles, the catalyticmetal compound, and the alkyl amine can be mixed in a container,preferably a closed glass container, with a magnetic stirring rod.Alternatively, the mixture can be mixed by shaking the container with amachine or by hand. The two types of M_(h)O_(i) nanoparticles, thecatalytic metal compound, and the alkyl amine are mixed until thereaction is substantially complete, which may be indicated by anexothermic reaction (i.e., heat release) and/or by a color change of themixture. After the reaction between the two types M_(h)O_(i)nanoparticles, the catalytic metal compound, and the alkyl amine iscomplete, the mixture is allowed to air dry. Subsequently, the mixtureis dried under a vacuum (about 5×10⁻² torr) for less than 12 hours.

Another representative method includes mixing M1_(h1)M2_(h2)O_(i) withcatalytic metal compound, and an excess of a solution having at leastone type of alkyl amine. The solution can also contain hydrazine and/orammonia. Subsequently, the M1_(h1)M2_(h2)O_(i) nanoparticles, thecatalytic metal compound, and the alkyl amine can be mixed in acontainer, preferably a closed glass container, with a magnetic stirringrod. Alternatively, the mixture can be mixed by shaking the containerwith a machine or by hand. The M1_(h1)M2_(h2)O_(i) nanoparticles, thecatalytic metal compound, and the alkyl amine are mixed until thereaction is substantially complete, which may be indicated by anexothermic reaction (i.e., heat release) and/or by a color change of themixture. After the reaction of the M1_(h1)M2_(h2)O_(i) nanoparticles,the catalytic metal compound, and the alkyl amine is complete, themixture is allowed to air dry. Subsequently, the mixture is dried undera vacuum (about 5×10⁻² torr) for less than 12 hours.

M, M1, M2, M_(CAT), the catalytic metal compound, and the alkyl aminescorrespond to the descriptions provided above and will not be describedhere in any more detail.

EXAMPLE 1

The following is a non-limiting illustrative example of an embodiment ofthe present invention. This example is not intended to limit the scopeof any embodiment of the present invention, but rather is intended toprovide specific experimental conditions and results. Therefore, oneskilled in the art would understand that many experimental conditionscan be modified, but it is intended that these modifications are withinthe scope of the embodiments of the present invention.

This example discusses the formation of TiO_(2−x)N_(x) nanoparticles onthe order of seconds at room temperature employing the directnitridation of TiO₂ nanostructures using alkyl ammonium compounds.Photocatalytically active TiO_(2−x)N_(x) particles were produced, whichabsorb well into the visible region (i.e., from about 350 nm to 2000nm). The TiO_(2−x)N_(x) particles are (i) stable, (ii) inexpensive,(iii) have a conduction band minimum that is higher than the H₂/H₂Ocouple (described above), and (iv) can absorb most of the photons of thesolar spectrum.

TiO₂ nanoparticles prepared by the controlled hydrolysis of titanium(IV) tetraisopropoxide in water under deaerated conditions can vary insize between 3 and 11 nm and form a nearly transparent colloidalsolution, which is stable for extended periods under refrigeration.Extended exposure to air at room temperature or controlled heating at50° C. produces a mild agglomeration of the TiO₂ nanoparticles andresults in the formation of a virtually opaque gel. Both the initialTiO₂ nanoparticle colloidal solution and the agglomerated gel solutionare treated with an excess of triethylamine. The mixture is mixed with aTeflon®-coated magnetic stirrer (or shaken) in a small closed glasscontainer. A reaction is found to take place readily between the TiO₂nanoparticle colloidal solution and the triethylamine, which appears tobe complete within several seconds following heat release and theformation of a yellowish, partially opaque, mixture. Upon drying andexposure to a vacuum of 5×10⁻² Torr for several hours, the treated,initially transparent, nanoparticle solution forms deep yellowcrystallites whose transmission electron micrograph (TEM), highresolution (HR) TEM, and electron diffraction patterns are illustratedin FIGS. 1A and 1B. The treated, partially agglomerated, nanoparticlegel is found to form orange to orange-red crystallites. XRD and HR TEMsdemonstrate that both the treated nanoparticle structures corresponddominantly to the anatase crystalline form of TiO_(2−x)N_(x), as do theoriginal TiO₂ nanoparticle crystallites.

FIG. 2 compares (a) the optical reflectance spectrum for Degussa P25™TiO₂ (reported at an average size of 30 nm), onsetting sharply at about380 nm; (b) the reflectance spectrum for TiO_(2−x)N_(x) nanoparticles(3–11 nm), rising sharply at 450 nm; and (c) the corresponding spectrumfor TiO_(2−x)N_(x) partially agglomerated nanoparticles, rising sharplyat 550 nm.

In addition, PdCl₂ was introduced into another nitriding amine-TiO₂mixture. The corresponding transmission electron micrograph andphotoelectron spectra obtained for TiO_(2−x)N_(x) nanoparticles (3–11nm) with palladium incorporation (about 1 μg added to the nitridingsolution), demonstrated not only the effects of an increased nitrogenuptake but also the impregnation of the TiO_(2−x)N_(x) structure withreduced Pd nanostructures (TiO_(2−x)N_(x)[Pd]). Furthermore, it wasobserved that the TiO_(2−x)N_(x) anatase crystal structure was alsoconverted to alternate crystal phase forms (possible the octahedriteform) for some of the TiO_(2−x)N_(x) nanoparticles. TheTiO_(2−x)N_(x)[Pd] agglomerated nanoparticles, which are brown-black incolor, absorb radiation at wavelengths in the range of about 450 nm to2000 nm.

In contrast to the nanoparticle activity, no measurable reaction or heatrelease is observed as either distinct rutile or anatase TiO₂micropowders are treated directly with an excess of triethylamine. Thetreatment of DeGussa P25™ “nanopowder” (mean distribution of about 30nm) results in a much slower reactive process, over several hours, whichappears to decant the smaller nanoparticles from the material. Thetreatment forms a pale brown crystalline form, which yields a complexreflectance spectrum. The TiO₂ nanoparticle solutions also interactstrongly with hydrazine and to a lesser extent with an ammoniumhydroxide (NH₃) solution. However, the reaction with triethylamine isfound to be facile at room temperature leading to nitrogen incorporationinto the TiO₂ lattice to form TiO_(2−x)N_(x) nanoparticles when thedirect nitridation process is carried out at a nanometer scale.

The infrared spectra depicted in FIG. 3 demonstrate another aspect ofthe nitridation process. Specifically, there is no evidence forhydrocarbon incorporation in the final doped TiO₂ product. The IRspectrum shown in FIG. 3( a) corresponds to that for the trialkylamine,demonstrating, among other features, the clear alkyl C—H stretch region.In contrast, the IR spectrum shown in FIG. 3( b), corresponding to theyellow TiO_(2−x)N_(x) nanocrystallites (yielding a reflectance spectrumof about 450 nm) pressed into a KBr pellet, shows virtually no infraredspectra especially in the C—H stretch region. This indicates virtuallyno residual organic incorporation after the air and vacuum dryingprocesses have been performed on the nitrided TiO₂ nanoparticles. Thisobservation is consistent both with photoelectron (XPS) and X-raydiffraction (XRD) studies.

XPS studies detect the presence of nitrogen not only at the surface, butalso incorporated into the TiO_(2−x)N_(x) nanoparticle agglomerates overa range from about 2.5 to 5.1 atomic % and increasing from about 7.5 to17.1 atomic % for the Pd treated samples. XPS spectra for TiO₂ andTiO_(2−x)N_(x) are compared in FIG. 4. The indicated nitrogenconcentrations above should be compared to less than 1 atomic % for avirgin TiO₂ powder. The XRD data taken for TiO₂ (FIG. 5A) and thenitrided partially agglomerated TiO₂ gel solution (FIG. 5B) show theeffects of a clear expansion of the “a” lattice parameter, duepresumably to nitrogen incorporation. XRD is a sensitive tool fordetermining whether the nitrogen dopants are actually incorporated oninterstitial lattice sites of the TiO₂ particles, or merely adsorbed atthe surface. Nitrogen doping was found to lead to a measurable increaseof the interplanar spacings in the agglomerated TiO₂ particles and peakbroadening, which can be attributed to the strain fields ofinterstitially dissolved nitrogen atoms and also the breaking at theTiO₂ lattice structure. The analysis of the XRD patterns demonstratesthe presence of a dominant anatase phase in both the untreated TiO₂nanoparticles and the doped samples (Table 1 below) for either thenitrided TiO₂ nanoparticles (3–11 nm) or partially agglomerated TiO₂nanoparticle samples. In this case no evidence for any degree ofconversion from the anatase to the rutile structure was found.

TABLE 1 A, standard c, standard Sample Phase a, (A) error (A) c (A)error (A) None Processed Rutile 4.5986 .0006 2.9634 .0006 TiO₂ Anatase3.7862 .0004 9.5070 .0011 Orange TiO₂ Anatase 3.7942 00.32 9.4676 .0075

However, the XRD pattern, observed for the nitrided TiO₂ nanoparticles(3–11 nm) treated with palladium is broad and complex, and demonstratesnot only the formation of the Pd crystallites but also an apparentconversion from the anatase structure to an alternate phase, which maybe, in part, the analog of the tetragonal octahedrite structure ofT_(i)O₂. The TEM micrographs of FIGS. 6A and 6B demonstrate both theimpregnation of the T_(i)O_(2−x)N_(x) structure with smaller “reduced”palladium nanoparticles, as well as the formation of a significantadditional alternate structure. The Pd treated samples appear black incolor, indicating that they absorb well into the near infrared region.

Photocatalytic activity was evaluated by measuring the decomposition ofmethylene blue at 390 and 540 nm, respectively, using a Clark MXR™ 2001femtosecond laser producing a 1 khz pulse train of 120 femtosecondpulses. The laser output was used to pump either an optical parametricamplifier to obtain tunable wavelengths in the visible spectrumincluding 540 nm or a second harmonic generation crystal to produce 390nm.

FIG. 7A illustrates the photodegradation observed at 390 nm formethylene blue in water at ph 7. The data for the nitrided TiO₂nanoparticle samples, as well as the palladium treated TiO₂nanoparticles referred to above, are consistent with a notably enhancedactivity for the TiO_(2−x)N_(x) nanoparticle constituencies at 390 nm.FIG. 7B illustrates the photodegradation observed at 540 nm in which thepartially agglomerated nitrided TiO_(2−x)N_(x) and palladium treatedTiO₂ nanoparticle samples still display a notable activity, whereas theactivity for TiO₂ nanoparticle is considerably muted. In contrast, atwavelengths below 350 nm, the activity of both the TiO₂ nanoparticlesand nitrided TiO₂ nanoparticle samples is comparable. Thus, nitridedTiO_(2−x)N_(x) nanoparticle samples, which can be generated in severalseconds at room temperature, are catalytically active at considerablylonger wavelengths than TiO₂ nanoparticles.

These results demonstrate that by forming and adjusting an initial TiO₂nanoparticle size distribution and mode of nanoparticle treatment, it ispossible to tune and extend the absorption of a doped TiO_(2−x)N_(x)sample well into the visible region. Further, these results indicatethat an important modification of a TiO₂ photocatalyst can be madeconsiderably simpler and more efficient by extension to the nanometerregime. The current process can produce submicrometer agglomerates of adesired visible light-absorbing TiO_(2−x)N_(x) nanoparticle via a roomtemperature procedure, which otherwise is highly inefficient, if notinoperative, at the micron scale.

EXAMPLE 2

The following is a non-limiting illustrative example of an embodiment ofthe present invention. This example is not intended to limit the scopeof any embodiment of the present invention, but rather is intended toprovide specific experimental conditions and results. Therefore, oneskilled in the art would understand that many experimental conditionscan be modified, but it is intended that these modifications are withinthe scope of the embodiments of the present invention.

This example discusses the formation of ZrO_(2−x)N_(x) nanoparticles atroom temperature employing the direct nitridation of ZrO₂ nanostructuresusing alkyl ammonium compounds. An excess volume of triethyl amine wasadded to a powder of zirconium dioxide (ZrO₂) nanoparticles and thismixture subsequently treated with PdCl₂. The mixture was mixed with aTeflon®-coated magnetic stirrer (or shaken) in a small closed glasscontainer. A reaction was found to take place readily between the ZrO₂powder/nanoparticles and the triethylamine and appears to quicklycomplete following heat release and the formation of a yellowish,partially opaque, mixture. Upon drying and exposure to a vacuum of5×10⁻² Torr for several hours, the treated, initially white collodial,nanoparticle solution forms pale yellow crystallites. The change incolor appears to indicate that nitrogen incorporation into the ZrO₂powder has occurred to form ZrO_(2−x)N_(x) nanostructures.

It should be emphasized that the above-described embodiments of thepresent invention, particularly, any “preferred” embodiments, are merelypossible examples of implementations, merely set forth for a clearunderstanding of the principles of the invention. Many variations andmodifications may be made to the above-described embodiment(s) of theinvention without departing substantially from the spirit and principlesof the invention. All such modifications and variations are intended tobe included herein within the scope of this disclosure and the presentinvention and protected by the following claims.

1. A method comprising: providing at least one M_(h)O_(i) nanoparticle,wherein h is in the range of about 1 to 3 and i is in the range of about1 to 5; providing a solution of an alkyl amine; mixing the at least oneM_(h)O_(i) nanoparticle and the solution of alkyl amine until a reactionbetween the at least one M_(h)O_(i) nanoparticle and alkyl amine issubstantially complete; and forming a M_(x)O_(y)N_(z) nanoparticle,wherein M is selected from the group consisting of: a metal, ametalloid, a lanthanide, and an actinide, wherein x is in the range ofabout 1 to 3, y is in the range of about 0.5 to less than 5, and z is inthe range of about 0.001 to 0.5.
 2. The method of claim 1, furthercomprising: providing a catalytic metal compound; and mixing thecatalytic metal compound with the at least one M_(h)O_(i) nanoparticleand the solution of alkyl amine until the reaction between the at leastone M_(h)O_(i) nanoparticle, alkyl amine, and catalytic metal compoundis substantially complete.
 3. The method of claim 1, wherein mixingincludes: mixing the at least one M_(h)O_(i) nanoparticle and thesolution of alkyl amine for about 10 seconds.
 4. The method of claim 1,further comprising: drying a product of the reaction between the atleast one M_(h)O_(i) nanoparticle and the solution of alkyl amine in avacuum for less than about 12 hours.
 5. The method of claim 1, whereinthe alkyl amine is N(R₁)(R₂)(R₃), wherein each of R₁, R₂, and R₃ isselected from the group consisting of: a methyl group, an ethyl group, apropyl group, and a butyl group.
 6. The method of claim 1, whereinproviding at least one M_(h)O_(i) nanoparticle includes: providing atleast one colloidal solution of at least one M_(h)O_(i) nanoparticle. 7.The method of claim 1, wherein providing at least one M_(h)O_(i)nanoparticle includes: providing at least one M_(h)O_(i) nanoparticledispersed in a gel solution.
 8. The method of claim 1, wherein providingat least one M_(h)O_(i) nanoparticle includes: providing at least onecolloidal solution of at least one M_(h)O_(i) nanoparticle, wherein thenanoparticle has a size less than about 40 nm.
 9. The method of claim 1,wherein providing at least one M_(h)O_(i) nanoparticle includes:providing at least one M_(h)O_(i) nanoparticle, wherein the nanoparticlehas a size less than about 40 nm.
 10. The method of claim 1, whereinmixing the at least one M_(h)O_(i) nanoparticle and the solution ofalkyl amine includes: mixing the at least one M_(h)O_(i) nanoparticlewith the solution of alkyl amine, wherein the alkyl amine is in excessof the at least one M_(h)O_(i) nanoparticle.
 11. The method of claim 1,wherein M is a metal.
 12. The method of claim 1, wherein M is ametalloid.
 13. A method comprising: providing at least two M_(h)O_(i)nanoparticles, wherein h is in the range of about 1 to 3 and i is in therange of about 1 to 5 and wherein each of the at least two M_(h)O_(i)nanoparticles are different; providing a solution of an alkyl amine;mixing the at least two M_(h)O_(i) nanoparticles and the solution ofalkyl amine until a reaction between the at least two M_(h)O_(i)nanoparticles and alkyl amine is substantially complete and forming aM1_(x1)M2_(x2)O_(y)N₂ nanoparticle, wherein each of M, M1, and M2, areselected from the group consisting of: a metal, a metalloid, alanthanide, and an actinide, wherein x1 is in the range of about 1 to 3,x2 is in the range of about 1 to 3, y is in the range of about 0.5 toless than 5, and z is in the range of about 0.001 to 0.5.
 14. The methodof claim 13, further comprising: providing a catalytic metal compound;and mixing the catalytic metal compound with the at least two M_(h)O_(i)nanoparticles and the solution of alkyl amine until the reaction betweenthe at least two M_(h)O_(i) nanoparticles, the alkyl amine, and thecatalytic metal compound is substantially complete.
 15. The method ofclaim 13, wherein mixing includes: mixing the at least two M_(h)O_(i)nanoparticles and the solution of alkyl amine for about 10 seconds. 16.The method of claim 13, further comprising: drying a product of thereaction between the at least two M_(h)O_(i) nanoparticles and thesolution of alkyl amine in a vacuum for less than about 12 hours. 17.The method of claim 13, wherein the alkyl amine is N(R₁)(R₂)(R₃),wherein each of R₁, R₂, and R₃ is selected from the group consisting of:a methyl group, an ethyl group, a propyl group, and a butyl group. 18.The method of claim 13, wherein providing at least two M_(h)O_(i)nanoparticles includes: providing at least one colloidal solution of atleast two M_(h)O_(i) nanoparticles.
 19. The method of claim 13, whereinmixing the at least two M_(h)O_(i) nanoparticles and the solution ofalkyl amine includes: mixing the at least two M_(h)O_(i) nanoparticieswith the solution of alkyl amine, wherein the alkyl amine is in excessof the at least two M_(h)O_(i) nanoparticles.
 20. The method of claim13, wherein M is a metal.
 21. The method of claim 13, wherein M is ametalloid.
 22. A method comprising: providing at least oneM1_(h1)M2_(h2)O_(i) nanoparticle, wherein h1 is in the range of about 1to 3, h2 is in the range of about 1 to 3, and i is in the range of about1 to 5; providing a solution of an alkyl amine; mixing the at least oneM1_(h1)M2_(h2)O_(i) nanoparticle and the solution of alkyl amine untilthe reaction between the at least one M1_(h1)M2_(h2)O_(i) nanoparticleand alkyl amine is substantially complete; and forming aM1_(x1)M2_(x2)O_(y)N_(z) nanoparticle, wherein each of M1 and M2 areselected from the group consisting of: a metal, a metalloid, alanthanide, and an actinide, wherein x1 is in the range of about 1 to 3,x2 is in the range of about 1 to 3, y is in the range of about 0.5 toless than 5, and z is in the range of about 0.001 to 0.5.
 23. The methodof claim 22, further comprising: providing a catalytic metal compound;and mixing the catalytic metal compound with the at least oneM1_(h1)M2_(h2)O_(i) nanoparticle and the solution of alkyl amine untilthe reaction between the at least one M1_(h1)M2_(h2)O_(i) nanoparticle,the alkyl amine, and the catalytic metal compound is substantiallycomplete.
 24. The method of claim 22, wherein mixing includes: mixingthe at least one M1_(h1)M2_(h2)O_(i) nanoparticle and the solution ofalkyl amine for about 10 seconds.
 25. The method of claim 22, furthercomprising: drying a product of the reaction between the at least oneM1_(h1)M2_(h2)O_(i) nanoparticle and the solution of alkyl amine in avacuum for less than about 12 hours.
 26. The method of claim 22, whereinthe alkyl amine is N(R₁)(R₂)(R₃), wherein each of R₁, R₂, and R₃ isselected from the group consisting of: a methyl group, an ethyl group, apropyl group, and a butyl group.
 27. The method of claim 22, whereinproviding at least one M1_(h1)M2_(h2)O_(i) nanoparticle includes:providing at least one colloidal solution of at least oneM1_(h1)M2_(h2)O_(i) nanoparticle.
 28. The method of claim 22, whereinmixing the at least one M1_(h1)M2_(h2)O_(i) nanoparticle and thesolution of alkyl amine includes: mixing the at least oneM1_(h1)M2_(h2)O_(i) nanoparticle with the solution of alkyl amine,wherein the alkyl amine is in excess of the at least oneM1_(h1)M2_(h2)O_(i) nanoparticle.
 29. The method of claim 22, wherein Mis a metal.
 30. The method of claim 22, wherein M is a metalloid.